Crystal structure and Rietveld refinement using X-ray powder diffraction data of two potassium and ammonium–samarium condensed phosphates: KSmHP3O10 and NH4SmHP3O10

Abstract

The structure of KSmHP3O10 has been determined by a single crystal X-ray analysis and has been solved by using 3299 independent reflections with a final R value of 0.019. This condensed phosphate crystallizes in the triclinic space group P1 with unit cell parameters a=6.956(2) Å, b=7.711(1) Å, c=8.570(2) Å, α=106.64(2)°, β=106.63(2)°, γ=82.47(3)°, V=421.4(2) Å3 and Dcal=3.494 g cm−3 for Z=2. The structure of NH4SmHP3O10–ammonium samarium hydrogen triphosphate has been determined from conventional X-ray powder diffraction data using the Rietveld method, with the isostructural compounds KSmHP3O10 and NH4BiHP3O10 as starting model. The cell is triclinic (space group P1Z=2), with a=6.9782(2) Å, b=7.7578(2) Å, c=8.6230(3) Å, α=106.354(2)°, β=105.961(2)°, γ=82.471(2)°, V=429.93(7) Å3 and Dcal=3.26 g cm−3. Refinement of 83 parameters by the Rietveld method, using 2547 reflections, leads to cRwp=0.152, cRp=0.117 and RB=0.0437. The unit cell contains two P3O105− groups linked with OH…O hydrogen bonding along the c axis. The samarium atoms in a eightfold co-ordination build infinite chains of edge-sharing SmO8 polyhedra running parallel to the a axis. The cations in this structure (K+ and NH4+) are located between chains formed of (HP3O104−) to form two dimensional zig zag sheets. The two polyhedra (SmO8 and KO10 or (NH4)O10) are connected by P3O105− to built a three dimensional network.